System and Method for Power Control Command for Device-to-Device Transmissions

ABSTRACT

A transmit power control rule for device-to-device (D2D) transmissions may not be necessary during periods in which no uplink transmissions are scheduled to be received by an enhanced Node B base station (eNB). When uplink transmissions are not scheduled to be received by the eNB, the eNB may send a transmit power control (TPC) command to a D2D capable user equipment (D2D UE) that instructs the D2D UE to perform a D2D transmission at a pre-defined transmit power level (e.g., maximum transmit power level). When uplink transmissions are scheduled to be received the eNB, the eNB may send a TPC command to the D2D UE that instructs the D2D UE to perform a D2D transmission at a transmit power level defined by a power control rule.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.15/377,525, filed on Dec. 13, 2016, which is a continuation of Ser. No.14/704,382, filed May 5, 2015, (now U.S. Pat. No. 9,642,099, issued May2, 2017), which claims the benefit of U.S. Provisional Application No.61/990,510, filed on May 8, 2014, all of which applications are herebyincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a system and method for wirelesscommunications, and, in particular embodiments, to a system and methodfor power control command for device-to-device transmissions.

BACKGROUND

Device-to-device (D2D) transmission techniques provide directcommunications between user equipments (UEs). D2D transmissiontechniques may increase system capacity and spectral efficiency, forinstance by offloading local communications from an enhanced Node B(eNB). In addition, D2D transmission techniques may also provide adirect connection between neighboring UEs when an indirect connectionvia an eNB is undesirable or unavailable.

There are two main steps to establish D2D transmissions. In the firststep, a device-to-device capable user equipment (D2D UE) attempts todiscover neighboring UEs. In the second step, the D2D UE directlycommunicates data with neighboring UEs without the data relaying throughthe eNB. Discovery can be performed as a standalone operation. D2Ddirect communication can be performed following D2D discovery.

D2D transmissions may be communicated over uplink resources, andtherefore have the potential to interfere with uplink signals receivedat nearby eNBs. Accordingly, an efficient power control scheme for D2Dtransmissions that mitigates interference to neighboring UEs and nearbyeNBs is desired.

SUMMARY

Technical advantages are generally achieved, by embodiments of thisdisclosure which describe system and method for power control commandfor device-to-device transmissions.

In accordance with an embodiment, a method for power control command fordevice-to-device (D2D) communications in a wireless communicationnetwork is provided. In this example, the method comprises establishinga link with a first user equipment (UE) in a cell. The first UE isconfigured to perform a D2D transmission to one or more UEs. The methodfurther comprises sending a transmit power control (TPC) command to thefirst UE. The TPC command instructing the first UE to perform the D2Dtransmission either at a pre-defined transmit power level or at atransmit power level defined by a power control rule. An apparatus forperforming this method is also provided.

In accordance with another embodiment, another method for power controlcommand for device-to-device (D2D) communications in a wirelesscommunication network is provided. In this example, the method comprisesreceiving a TPC command from a base station. The TPC command instructsthe first UE to perform a D2D transmission either at a pre-definedtransmit power level or at a transmit power level defined by a powercontrol rule. The method further comprises performing the D2Dtransmission using the pre-defined transmit power level when the TPCcommand instructs the first UE to perform the D2D transmission at thepre-defined transmit power level. The method further comprisesperforming the D2D transmission at the transmit power level defined bythe power control rule when the TPC command instructs the UE to performthe D2D transmission at the transmit power level defined by the powercontrol rule. An apparatus for performing this method is also provided.

In accordance with yet another embodiment, a method for power controlcommand for setting a transmit power level in a D2D transmission isprovided. In this example, the method comprises receiving a TPC commandfrom a base station. The TPC command instructs the first UE to perform aD2D transmission either at a pre-defined transmit power level or at atransmit power level defined by a power control rule. The method furthercomprises obtaining the transmit power level in accordance withP_(D2D)=min{P_(CMAX,D2D), 10 log₁₀(M)+P_(O) _(_) _(D2D,1)+α·PL} [dBm],where P_(CMAX,D2D) is a maximum power level of a D2D communicationchannel, M is a bandwidth of a D2D communication channel resourceassignment, PL is a downlink path loss estimate calculated for a servingcell, and P_(O) _(_) _(D2D) and α are provided by higher layerparameters. An apparatus for performing this method is also provided.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawing, in which:

FIG. 1 illustrates a diagram of an embodiment wireless network;

FIG. 2 illustrates a diagram of an embodiment wireless network forsupporting direct device-to-device (D2D) communication;

FIG. 3 illustrates a flow chart of an embodiment method for regulating atransmit power level of D2D transmissions;

FIG. 4 illustrates a flow chart of an embodiment method for performingD2D transmissions;

FIG. 5 illustrates a flow chart of an embodiment method for setting atransmit power level;

FIG. 6 illustrates a flow chart of an embodiment method for transmittinga transmit power control (TPC) command to a UE;

FIG. 7 illustrates a flow chart of an embodiment method for performingD2D transmissions;

FIG. 8 illustrates a flow chart of another embodiment method forperforming D2D transmissions;

FIG. 9 illustrates a block diagram of an embodiment communicationsdevice; and

FIG. 10 illustrates a block diagram of an embodiment computing platform.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the embodiments andare not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The structure, manufacture and use of the embodiments are discussed indetail below. It should be appreciated, however, that the presentinvention provides many applicable inventive concepts that can beembodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

A base station may communicate transmit power control (TPC) commands touser equipments (UEs) to instruct the UEs to regulate their transmitpower level based on transmit power control algorithms/rules. For D2Dtransmissions, transmit power control rules may typically specifyrelatively low transmit power levels for UEs located nearby the eNB tomitigate interference between the UE's D2D transmissions and uplinktransmissions being received by the eNB from UEs. However, restrictingthe D2D UE to low power D2D transmissions may be unnecessary duringperiods in which no uplink transmissions are scheduled to be received bythe eNB. In addition, the eNB may tolerate a predetermined amount ofinterference from D2D transmissions to improve D2D transmissionperformance. This may be beneficial when the D2D transmissions are usedfor the purpose of public safety. Thus, regulating D2D transmissionsusing a transmit power control rule may unnecessarily constrain D2Dperformance (e.g., throughput, range, etc.) during periods in which nouplink transmissions are received by the eNB. In such cases, it may bedesirable to improve D2D performance and/or range by using a pre-definedtransmit power level (e.g., a maximum transmit power level) to performD2D transmissions.

Aspects of this disclosure provide an embodiment TPC command thatinstructs a D2D UE to perform a D2D transmission either at a pre-definedtransmit power level or based on a power control rule depending onwhether uplink transmissions are scheduled to be received by an eNBduring a specific period. The TPC command may instruct the D2D UE toperform the D2D transmission at the pre-defined transmit power level(e.g., a maximum transmit power level) when there is no uplinktransmissions scheduled to be received by the eNB over time-frequencyresources available to carry the D2D transmission. Conversely, the TPCcommand may instruct the D2D UE to perform a D2D transmission at atransmit power level defined by a power control rule when uplinktransmissions are scheduled to be received by the eNB overtime-frequency resources available to carry the D2D transmission. TheTPC command may be transmitted in a physical downlink control channel(PDCCH) or an enhanced PDCCH (ePDCCH) using a downlink controlinformation (DCI) format. In one embodiment, a DCI format 3/3A (asdefined in LTE specifications) may carry a TPC command thatenables/disables a transmit power control rule for a D2D UE. The TPCcommand may carry a new radio network temporary identifier (RNTI)(referred to as a D2D-TPC-RNTI) to identify the D2D UE and/or todistinguish the new TPC command from existing control commands (e.g.,LTE control commands). In another embodiment, a new DCI format (e.g.,DCI format 5) may be defined to instruct the D2D UE to perform the D2Dtransmission to neighboring UE at either a pre-defined transmit powerlevel or a transmit power level defined by a power control rule. Inaddition, the eNB may notify the UE about a specific period for whichthe UE's D2D transmissions can be communicated at a pre-defined transmitpower. In one embodiment, the eNB communicates the specific period tothe D2D UE via a parameter in a downlink control channel. In anotherembodiment, the eNB communicates the time interval to the D2D UE usinghigher-layer signaling. As a result, the D2D UE may use a pre-definedtransmit power level to perform D2D transmissions during the specificperiod. These and other details are described in greater detail below.

FIG. 1 illustrates a wireless network 100 for communicating data. Thewireless network 100 includes an access point (AP) no having a coveragearea 101, a plurality of mobile devices 120, and a backhaul network 130.The AP 110 may comprise any component capable of providing wirelessaccess by, among other things, establishing uplink (dashed line) and/ordownlink (dotted line) connections with the UEs 120, such as a basestation, an enhanced base station (eNB), a femtocell, and otherwirelessly enabled devices. The UEs 120 may comprise any componentcapable of establishing a wireless connection with the AP 110, such as amobile phone, a mobile station or other wirelessly enabled devices. Thebackhaul network 130 may be any component or collection of componentsthat allow data to be exchanged between the AP 110 and a remote end. Insome embodiments, there may be multiple such networks, and/or thenetwork may comprise various other wireless devices, such as relays, lowpower nodes, etc.

FIG. 2 illustrates a wireless network 200 for supporting direct D2Dcommunications. As shown, the wireless network 200 comprises an eNB 205and a plurality of UEs 210, 220, 230. In this example, the UE 210performs a D2D transmission 212 to the UE 220. Oftentimes, the eNBs willbe operated by, or under the control of, a wireless service provider,and hence may allow the wireless service provider to monitor and/orcontrol various aspects of a direct D2D communication between a pair ofUEs. For instance, one or both of the UEs 210, 220 may establish acellular uplink (Cell_UL) connection with the eNB 205, thereby allowingthe wireless service provider to monitor various aspects of the D2Dtransmission 212. Likewise, the eNB 205 may establish a cellulardownlink (Cell_DL) connection with one or both of the UEs 210, 220,thereby allowing the wireless service provider to control variousaspects of the D2D communication. The D2D transmission 212 may becommunicated over uplink resources (e.g., uplink frequencies, etc.), andtherefore may interfere with uplink signals being received by the eNB205. For example, the D2D transmission 212 may interfere with an uplinktransmission 235 from the UE 230. This interference may be particularlyproblematic when the UE 210 is positioned nearby the eNB 205.Interference may also be present when the UE 210 is located somewhatfurther from the eNB 205, but uses a high transmit power level. The UE210 may perform the D2D transmission 212 using a transmit power leveldefined by a transmit power control algorithm/rule (e.g., open-looppower control algorithm defined in LTE specifications). The transmitpower control algorithm may constrain a transmit power level of the D2Dtransmission 212 to mitigate interference between the D2D transmission212 and the uplink transmission 235. However, constraining the transmitpower level of the D2D transmission 212 in accordance with the transmitpower control rule may unnecessarily reduce D2D performance duringperiods in which no uplink transmissions are scheduled to be received bythe eNB 205.

Aspects of this disclosure address this issue by providing a transmitpower control (TPC) command that instructs the UE 210 to perform D2Dtransmissions at a pre-defined transmit power level (e.g., a maximumtransmit power level) during a periods in which no uplink transmissionsare scheduled to be received. FIG. 3 illustrates a flow chart of anembodiment method 300 for regulating transmit power levels of D2Dtransmissions, as might be performed by an eNB. As shown, the method 300begins at step 310, where the eNB establishes a link with a UE that isconfigured to perform a D2D transmission. Subsequently, the method 300proceeds to step 320, where the eNB sends a transmit power control (TPC)command that instructs the UE to perform the D2D transmission at eithera pre-defined transmit power level or a transmit power level defined bya transmit power control rule. The TPC command may instruct the UE toperform the D2D transmission at the pre-defined transmit power levelwhen no uplink transmissions are scheduled to be received by the eNB.Alternatively, the eNB transmitting the TPC command may instruct the UEto perform the D2D transmission at the transmit power level defined bythe power control rule when uplink transmissions are scheduled to bereceived by the eNB. In an embodiment, parameters of the power controlrule (e.g., open-loop power control rule, closed-loop power controlrule, etc.) are configured by higher layer signaling. The TPC commandmay instruct the UE to use the pre-defined power level, or the powercontrol rule, for a specific period (e.g., T subframes). The specificperiod may be specified by a parameter in the TPC command.Alternatively, the specific period may be communicated to the UE viahigher-layer signaling. The TPC command may be transmitted on a physicaldownlink control channel (PDCCH) and/or an enhanced physical downlinkcontrol channel (EPDCCH). The TPC command may be communicated using adownlink control information (DCI) format e.g., a new DCI format, anexisting DCI format carrying a new radio network temporary identifier(RNTI) associated with a D2D UE, etc.

FIG. 4 illustrates a flow chart of an embodiment method 400 forperforming D2D transmissions, as might be performed by a UE. As shown,the method 400 begins at step 410, where a UE receives a TPC commandfrom a base station that instructs the UE to perform a D2D transmissioneither at a pre-defined transmit power level or at a transmit powerlevel defined by a power control rule. Thereafter, the method 400proceeds to step 420, where the UE determines whether the TPC commandinstructs the UE to perform D2D transmission using the power controlrule. If so, the method 400 proceeds to step 440, where the UE performsthe D2D transmission at the transmit power level defined by the powercontrol rule. Alternatively, if the TPC command instructs the UE not toperform D2D transmission using a power control rule, the method 400proceeds to step 430, where the UE determines whether D2D transmissioncoincides with a random access channel (RACH) transmission. If so, themethod 400 proceeds to step 440. A D2D transmission may coincide with aRACH transmission when the D2D transmission collides, or significantlyinterferes, with the RACH transmission. Alternatively, if the D2Dtransmission does not coincide with the RACH transmission, then themethod 400 proceeds to step 450, where the UE performs D2D transmissionusing the pre-defined transmit power level. For instance, in someembodiments the D2D transmission may be performed over time-frequencyresources of a D2D communication channel, e.g., a physical sidelinkshared channel (PSSCH). In some embodiments, the UE may not considerwhether the D2D transmission coincides with a RACH transmission. In suchembodiments, step 430 is omitted, and the method 400 proceeds to step450 when the TPC command instructs the UE not to perform D2Dtransmission using a power control rule.

FIG. 5 illustrates a flow chart of an embodiment method 500 for settinga transmit power level, as might be performed by a UE. As shown, themethod 500 begins at step 510, where the UE receives a TPC command froma base station. In an embodiment, the UE performs a D2D transmission ata pre-defined transmit power level when the TPC command instructs the UEto perform the D2D transmission at the pre-defined transmit power level.In another embodiment, the UE performs a D2D transmission at a transmitpower level defined by a transmit power control rule when the TPCcommand instructs the UE to perform the D2D transmission in accordancewith the transmit power control rule. Subsequently, the method 500proceeds to step 520, where the UE obtains the transmit power level inaccordance with the equation P_(D2D)=min{P_(CMAX,D2D), 10 log₁₀(M)+P_(O)_(_) _(D2D,1)+α·PL} [dBm], where P_(D2D) is the transmit power levelused by the UE to perform the D2D transmission, P_(CMAX,D2D) is themaximum power the UE can transmit on the D2D communication channel whenthe open loop power control rule is used, M is a bandwidth of a D2Dcommunication channel resource assignment, PL is a downlink path lossestimate calculated for a serving cell, and P_(O) _(_) _(D2D) and α areprovided by higher layer parameters. In some embodiments, the D2Dcommunication channel is a PSSCH. In such embodiments, the aboveequation may be rewritten as P_(PSSCH)=min{P_(CMAX,PSSCH), 10log₁₀(M_(PSSCH))+P_(O) _(_) _(PSSCH,1)+α_(PSSCH,1)·PL}, whereP_(CMAX,PSSCH) is the maximum power the UE can transmit on the PSSCHwhen the open loop power control rule is used, M_(PSSCH) is a bandwidthof a PSSCH resource assignment, PL is a downlink path loss estimatecalculated for a serving cell, and P_(O) _(_) _(PSSCH,1) and α_(PSSCH,1)are provided by higher layer parameters.

FIG. 6 illustrates a flow chart of an embodiment method 600 fortransmitting a transmit power control (TPC) command to a UE. As shown,the method 600 begins at step 610, where an eNB determines whetheruplink transmissions have been scheduled from UEs in its cell for aspecific period (e.g., T subframes). If the eNB determines that at leastone UL transmission is scheduled during the specific period, then themethod 600 proceeds to step 620, where the eNB instructs the UE toperform D2D transmissions at a transmit power level defined by atransmit power control rule. In some embodiments, the eNB expresslyinstructs the UE to use a transmit power control rule by transmitting aTPC command that instructs the UE to use a transmit power control rule.In other embodiments, the UE has previously been instructed to use atransmit power control rule unless further notice is received (e.g., viaa TPC command disabling D2D power control). In such embodiments, the eNBimplicitly instructs the UE to continue using the transmit power controlrule by not transmitting a TPC command disabling a D2D power controlrule. During step 610, if the eNB determines that UL transmissions arenot scheduled during the specific period, then the method 600 proceedsto step 630, where the eNB sends the TPC command to instruct the UE toperform D2D transmissions at a pre-defined transmit power level (e.g., amaximum transmit power level). In another embodiment, the eNB instructsthe UE to perform D2D transmissions at a fixed transmit power level toprovide larger range D2D transmissions irrespective of theirinterference with uplink transmissions received by the eNB or otherwireless communications.

FIG. 7 illustrates a flow chart of an embodiment method 700 forperforming D2D transmissions. As shown, the method 700 begins at step710, where a UE begins performing D2D transmissions at a transmit powerlevel defined by a transmit power control rule. Thereafter, the methodproceeds to step 720, where the UE determines whether a TPC commanddisabling the transmit power control rule has been received. If so, themethod 700 proceeds to step 730, where the UE performs D2D transmissionsat a pre-defined transmit power level. Alternatively, if a TPC commanddisabling the transmit power control rule has not been received, thenthe method 700 proceeds to step 740, where the UE performs D2Dtransmissions at the transmit power level defined by the transmit powercontrol rule.

FIG. 8 illustrates a flow chart of another embodiment method 800 forperforming D2D transmissions associated with a random access channel(RACH) transmission. As shown, the method 800 begins at step 810, wherea UE begins performing D2D transmissions at a transmit power leveldefined by a transmit power control rule. Thereafter, the method 800proceeds to step 820, where the UE determines whether a TPC commanddisabling the transmit power control rule has been received. If not, themethod 800 proceeds to step 830, where the UE performs D2D transmissionsat the transmit power level defined by the transmit power control rule.Alternatively, if a TPC command disabling the transmit power controlrule has been received, then the method 800 proceeds to step 840, wherethe UE determines the D2D transmissions would coincide (e.g., collide)with a random access channel (RACH) transmission. If not, the method 800proceeds to step 850, where the UE performs D2D transmissions using apre-defined transmit power level. Alternatively, if the D2D transmissionwould coincide with a RACH transmission, then the method 800 proceeds tostep 860, where the UE performs the D2D transmission at the transmitpower level defined by the transmit power control rule.

FIG. 9 is a block diagram of a processing system 900 that may be usedfor implementing the devices and methods disclosed herein. Specificdevices may utilize all of the components shown, or only a subset of thecomponents, and levels of integration may vary from device to device.Furthermore, a device may contain multiple instances of a component,such as multiple processing units, processors, memories, transmitters,receivers, etc. The processing system 900 may comprise a processing unitequipped with one or more input/output devices, such as a speaker,microphone, mouse 924, touchscreen, keypad, keyboard 924, printer 924,display 916, and the like. The processing system 900 may include acentral processing unit (CPU) 902, memory 910, a mass storage device904, a video adapter 915, and an I/O interface 921, all connected to abus 906.

The bus 906 may be one or more of any type of several bus architecturesincluding a memory bus or memory controller, a peripheral bus, videobus, or the like. The CPU 902 may comprise any type of electronic dataprocessor. The memory 910 may comprise any type of non-transitory systemmemory such as static random access memory (SRAM), dynamic random accessmemory (DRAM), synchronous DRAM (SDRAM), read-only memory (ROM), acombination thereof, or the like. In an embodiment, the memory 910 mayinclude ROM for use at boot-up, and DRAM for program and data storagefor use while executing programs.

The mass storage device 904 may comprise any type of non-transitorystorage device configured to store data, programs, and other informationand to make the data, programs, and other information accessible via thebus 906. The mass storage device 904 may comprise, for example, one ormore of a solid state drive, hard disk drive, a magnetic disk drive, anoptical disk drive, or the like.

The video adapter 915 and the I/O interface 921 provide interfaces tocouple external input and output devices to the processing system 900.As illustrated, examples of input and output devices include the display916 coupled to the video adapter 915 and the mouse/keyboard/printer 924coupled to the I/O interface 921. Other devices may be coupled to theprocessing system 900, and additional or fewer interfaces or interfacecards may be utilized. For example, a serial interface such as UniversalSerial Bus (USB) (not shown) may be used to provide an interface for aprinter 924.

The processing system 900 also includes one or more network interfaces907, which may comprise wired links, such as an Ethernet cable or thelike, and/or wireless links to access nodes or different networks 930.The network interface 907 allows the processing system 900 tocommunicate with remote units via the networks 930. For example, thenetwork interface 907 may provide wireless communication via one or moretransmitters/transmit antennas and one or more receivers/receiveantennas. In an embodiment, the processing system 900 is coupled to alocal-area network 930 or a wide-area network 930 for data processingand communications with remote devices, such as other processing units,the Internet, remote storage facilities, or the like.

FIG. 10 illustrates a block diagram of an embodiment of a communicationsdevice moo, which may be equivalent to one or more devices (e.g.,requesting devices, candidate devices, network nodes, etc.) discussedabove. The communications device 1000 may include a processor 1004, amemory 1006, a cellular interface 1010, a supplemental interface 1012,and a backhaul interface 1014, which may (or may not) be arranged asshown in FIG. 10. The processor 1004 may be any component capable ofperforming computations and/or other processing related tasks, and thememory 1006 may be any component capable of storing programming and/orinstructions for the processor 1004. The cellular interface 1010 may beany component or collection of components that allows the communicationsdevice 1000 to communicate using a cellular signal, and may be used toreceive and/or transmit information over a cellular connection of acellular network. The supplemental interface 1012 may be any componentor collection of components that allows the communications device 1000to communicate data or control information via a supplemental protocol.For instance, the supplemental interface 1012 may be a non-cellularwireless interface for communicating in accordance with aWireless-Fidelity (Wi-Fi) or Bluetooth protocol. Alternatively, thesupplemental interface 1012 may be a wireline interface. The backhaulinterface 1014 may be optionally included in the communications device1000, and may comprise any component or collection of components thatallows the communications device 1000 to communicate with another devicevia a backhaul network.

The following references are related to subject matter of the presentapplication. Each of these references is incorporated herein byreference in its entirety:

3GPP specification 36.213;

3GPP RAN1 Chairman Notes, RAN1#76;

3GPP RAN1 Chairman Notes, RAN1#76bis;

3GPP RAN1 Chairman Notes, RAN1#73.

While this invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications and combinations of theillustrative embodiments, as well as other embodiments of the invention,will be apparent to persons skilled in the art upon reference to thedescription. It is therefore intended that the appended claims encompassany such modifications or embodiments.

What is claimed is:
 1. A method for power control command fordevice-to-device (D2D) communications in a wireless communicationnetwork, the method comprising: receiving, by a user equipment (UE), aTPC command from a base station, the TPC command instructing the UE toperform a D2D transmission at a transmit power level defined by a powercontrol rule when the D2D transmission coincides with one or more uplinkrandom access channel (RACH) transmissions or at a pre-defined transmitpower level when the D2D transmission does not coincide with an uplinkRACH transmission, the transmit power level defined by the power controlrule being lower than the pre-defined transmit power level; performing,by the UE, the D2D transmission using the pre-defined transmit powerlevel when the TPC command instructs the UE to perform the D2Dtransmission at the pre-defined transmit power level; and performing, bythe UE, the D2D transmission at the transmit power level defined by thepower control rule when the TPC command instructs the UE to perform theD2D transmission at the transmit power level defined by the powercontrol rule.
 2. The method of claim 1, further comprising performingthe D2D transmission over a D2D communication channel.
 3. The method ofclaim 2, the D2D communication channel being a physical sidelink sharedchannel (PSSCH).
 4. The method of claim 1, further comprising receivingthe TPC command over either a physical downlink control channel (PDCCH)or an enhanced physical downlink control channel (EPDCCH).
 5. The methodof claim 1, the power control rule comprising an open-loop power controlrule.
 6. A user equipment (UE) for power control command fordevice-to-device (D2D) communications in a wireless communicationnetwork, the UE comprising: a non-transitory memory storage comprisinginstructions; and one or more processors in communication with thenon-transitory memory storage, wherein the one or more processorsexecute the instructions to: receive a TPC command from a base station,wherein the TPC command instructs the UE to perform a D2D transmissionat a transmit power level defined by a power control rule when the D2Dtransmission coincides with one or more uplink random access channel(RACH) transmissions or at a pre-defined transmit power level when theD2D transmission does not coincide with an uplink RACH transmission, thetransmit power level defined by the power control rule being lower thanthe pre-defined transmit power level; perform the D2D transmission usingthe pre-defined transmit power level when the TPC command instructs theUE to perform the D2D transmission at the pre-defined transmit powerlevel and when the D2D transmission does not coincide with a randomaccess channel (RACH) transmission; and perform the D2D transmission atthe transmit power level defined by the power control rule when the TPCcommand instructs the UE to perform the D2D transmission at the transmitpower level defined by the power control rule.
 7. The UE of claim 6,wherein the one or more processors execute the instructions to performthe D2D transmission over a D2D communication channel.
 8. The UE ofclaim 7, wherein the D2D communication channel is a physical sidelinkshared channel (PSSCH).
 9. The UE of claim 6, wherein the one or moreprocessors execute the instructions to receive the TPC command overeither a physical downlink control channel (PDCCH) or an enhancedphysical downlink control channel (EPDCCH).
 10. The UE of claim 6,wherein the power control rule comprises an open-loop power controlrule.
 11. A method for power control command for device-to-device (D2D)communications in a wireless communication network, the methodcomprising: receiving, by a user equipment (UE), a first TPC commandfrom a base station, the first TPC command instructing the UE to performa first D2D transmission at a transmit power level defined by a powercontrol rule; performing, by the UE, the first D2D transmission at thetransmit power level defined by the power control rule, the first D2Dtransmission coinciding with one or more uplink random access channel(RACH) transmissions; receiving, by the UE, a second TPC command fromthe base station, the second TPC command instructing the UE to perform asecond D2D transmission at a pre-defined transmit power level; andperforming, by the UE, the second D2D transmission at the pre-definedtransmit power level, the second D2D transmission not coinciding with anuplink RACH transmission, and the transmit power level defined by thepower control rule being lower than the pre-defined transmit powerlevel.
 12. The method of claim 11, further comprising performing thefirst and second D2D transmissions over a D2D communication channel. 13.The method of claim 12, the D2D communication channel being a physicalsidelink shared channel (PSSCH).
 14. The method of claim 11, furthercomprising receiving the first and second TPC commands over either aphysical downlink control channel (PDCCH) or an enhanced physicaldownlink control channel (EPDCCH).
 15. The method of claim 11, the powercontrol rule comprising an open-loop power control rule.
 16. A userequipment (UE) for power control command for device-to-device (D2D)communications in a wireless communication network, the UE comprising: anon-transitory memory storage comprising instructions; and one or moreprocessors in communication with the non-transitory memory storage,wherein the one or more processors execute the instructions to: receivea first TPC command from a base station, the first TPC commandinstructing the UE to perform a first D2D transmission at a transmitpower level defined by a power control rule; perform the first D2Dtransmission at the transmit power level defined by the power controlrule, the first D2D transmission coinciding with one or more uplinkrandom access channel (RACH) transmissions; receive a second TPC commandfrom the base station, the second TPC command instructing the UE toperform a second D2D transmission at a pre-defined transmit power level;and perform the second D2D transmission at the pre-defined transmitpower level, the second D2D transmission not coinciding with an uplinkRACH transmission, and the transmit power level defined by the powercontrol rule being lower than the pre-defined transmit power level. 17.The UE of claim 16, wherein the one or more processors execute theinstructions to perform the first and second D2D transmissions over aD2D communication channel.
 18. The UE of claim 17, wherein the D2Dcommunication channel is a physical sidelink shared channel (PSSCH). 19.The UE of claim 16, wherein the one or more processors execute theinstructions to receive the first and second TPC commands over either aphysical downlink control channel (PDCCH) or an enhanced physicaldownlink control channel (EPDCCH).
 20. The UE of claim 16, wherein thepower control rule comprises an open-loop power control rule.